1. Field of the Invention
The present invention relates to a thermal head used in a facsimile, various kinds of printers, a plotter, a printing device in a computer terminal, etc. in a thermosensible recording system or a thermal transfer recording system.
2. Description of the Related Art
In the thermal head of this kind, a plurality of heating resistors and electrodes corresponding to these heating resistors are disposed in a base member to selectively heat the heating resistors by providing a signal to the electrodes. A portion of a printing medium coated on a surface of a printed object is melted or sublimed by the heat of the heating resistors to perform a transferring operation by forming dots on the printed object.
Further, as shown in e.g., Japanese Patent Application Laying Open (KOKAI) No. 53-87240, etc., a slit is formed in a portion of the heating resistors to reliably form the dots. In this case, a heating amount is locally increased in the vicinity of four corners of the slit so that a portion of the printing medium approximately opposite to the four corners of the slit is first melted or sublimed and is widened in a radial shape, thereby printing one dot.
In the structure for forming the slit in the heating resistors, a large heating amount is locally obtained so that the accuracy in formation of the dots can be improved by melting or subliming the printing medium. However, the accuracy in circularity of the dots is reduced and density becomes irregular so that the quality of an image is reduced.
The shape of the slit gives a great influence to the accuracy in circularity of the obtained dots and the generation of the irregular density. In the structure mentioned above, since the slit is simply formed to locally obtain heat, it is not possible to take measures with respect to the reduction of the accuracy in circularity of the dots and the irregular density.